1. Field of the Invention
The present invention relates to a direct injection type fuel injection device adapted to inject fuel directly into a combustion chamber in an internal combustion engine. More particularly, the present invention is concerned with a direct injection type fuel injection device constructed such that fuel injected from a fuel injection valve and gas injected from a gas injection valve are brought into collision with each other.
The present invention also relates to a fuel injection control device applied to an internal combustion engine of a direct injection type wherein fuel is injected directly into a combustion chamber. More particularly, the present invention is also concerned with a fuel injection control device for an internal combustion engine which is constructed to control a fuel injection valve and a gas injection valve in such a manner that fuel injected into a combustion chamber from the fuel injection valve and gas injected into the combustion chamber from the gas injection valve are brought into collision with each other.
2. Description of Related Art
As conventional fuel injection systems, for example in the following Patent Literatures 1 and 2 there are disclosed fuel injection devices constructed such that fuel injected from a fuel injection valve and air injected from an air injection valve are brought into collision with each other.
In Patent Literature 1 it is described that, in a cylinder injection (direct injection) type spark ignition engine, a mounting angle of an air injection valve and that of a fuel injection valve are each set at an angle at which both injection axes cross each other in both vertical and horizontal directions and both injection directions face a cavity combustion chamber. It is described in Patent Literature 1 that, according to the construction, since the air injection axis and the fuel injection axes cross each other, fuel can be atomized at the time of fuel injection in an intake (suction) stroke, and since injected air is directed toward the interior of the cavity combustion chamber, it is possible to suppress the adhesion of fuel to the same chamber and hence possible to diminish the production of smoke and unburned HC.
On the other hand, in Patent Literature 2 it is described that, in an internal combustion engine of a fuel injection type though not a direct injection type, a pair of air assist orifices are formed so that their fuel injecting directions cross each other on both sides of a fuel injection orifice in a plane which substantially includes the fuel injection orifice. It is described in the same patent literature that, according to the above construction, a fuel flow jetted from the fuel injection orifice is narrowed by air flows from both sides thereof and becomes flat as a whole.
For attaining an optimal combustion performance in a direct injection type internal combustion engine, it is necessary to promote the atomization of fuel for the improvement of combustibility throughout the whole region of engine operating conditions. In a direct injection type internal combustion engine, moreover, in order to attain a combustion performance to match the start-up in the cold or to match a partial load operation, it is necessary to adjust a spray penetration distance (distance from a fuel injection orifice of a fuel injection valve up to a spray tip) and a spray shape.
There is known an internal combustion engine of a direct injection type wherein the pressure of fuel fed to a fuel injection valve is kept constant. In this case, when the internal combustion engine is started up in the cold, the wall surface temperature of a combustion chamber is low, so that the fuel injected from the fuel injection valve adheres to the wall surface of the combustion chamber and becomes difficult to evaporate, with a consequent fear that the combustion performance may be deteriorated, leading to a worsening of exhaust emission of the internal combustion engine.
In a partial load operation of the internal combustion engine, in order to realize an effective stratified charge combustion, it is necessary to create a fuel spray not yielding to an intake flow. In other words, it is necessary to form a fuel spray having a strong inertia force and a large spray penetration distance (distance from a fuel injection orifice of a fuel injection valve up to a spray tip at a certain time elapsed after the injection of fuel). Further, in a direct injection type internal combustion engine, in order to improve the intake efficiency by fuel evaporation cooling in the whole region of engine operating conditions, it is necessary to atomize a fuel spray.
In the internal combustion engine of a direct injection type, even in the case where the fuel pressure is made variable for the fuel injection valve, there has heretofore been a fear that the fuel pressure may not rise to a predetermined level but remain low at the time of start-up of the engine, with a consequent worsening of atomization of a fuel spray. Further, since the fuel injection valve usually employed has a fixed fuel injection orifice, it has so far been impossible to change the spray penetration distance and spray particle diameter of fuel although it has been possible to change the fuel pressure.
In a direct injection type internal combustion engine, therefore, at the time of start-up in the cold or in a full-load operation, it is necessary to promote the atomization of the whole of fuel spray and shorten the spray penetration distance, while in a partial load operation it is necessary to promote the atomization of the entire fuel spray and lengthen the spray penetration distance. Generally, the spray shape of fuel is set in conformity with the shape of a combustion chamber and therefore it is preferable that the spray shape be not changed or the spray penetration distance and the spray particle diameter be made variable while retaining the similarity of the spray shape.
In the following Patent Literature 3 there is disclosed a fuel injection device wherein fuel injected from a fuel injection valve and air injected from an air injection valve are correlated with each other. According to the fuel injection device disclosed therein, fuel and air can be jetted to the exterior each independently and there is obtained an optimal spray shape matching an operating condition of an internal combustion engine.                Patent Literature 1:        Japanese patent unexamined publication No. 2000-97032 (pages 5 and 6, FIGS. 10 and 11);        Patent Literature 2:        Japanese patent unexamined publication No. Hei 4(1992)-50469 (pages 2 to 6, FIG. 2);        Patent Literature 3:        Japanese patent unexamined publication No. Hei 11(1999)-280593 (pages 2 to 4, FIGS. 1 to 5).        
In the internal combustion engine described in the above Patent Literature 1, however, if a large amount of air corresponding to the amount of intake air is injected into collision with fuel at the time of stratified charge combustion (mainly in a partial load operation), the resulting air-fuel mixture is dispersed and it becomes impossible to stratify the mixture which is required for stratified charge combustion. Consequently, in stratified charge combustion, it is impossible to effect fuel atomization by air collision, with the result that it has so far been impossible to attain the atomization of fuel throughout the whole region of operating conditions required for obtaining an optimal combustion performance in a direct injection type internal combustion engine.
In the Patent Literatures 1 and 2 there is described no construction permitting adjustment of the spray penetration distance and the spray shape.
Therefore, for attaining a combustion performance matching the start-up in the cold of an internal combustion engine or matching a partial load operation of the engine, it has been impossible to adjust the spray penetration distance and the spray shape and hence impossible to improve the combustion performance.
Further, in the Patent Literatures 1 and 2 there merely is described the construction wherein air is brought into collision with a fuel spray. A construction wherein air is brought into collision uniformly with sprayed fuel to match the entire distribution of the sprayed fuel is neither described nor suggested therein. Thus, it has been impossible to atomize fuel more uniformly and finely as a whole and hence impossible to improve the combustion performance.
On the other hand, in the fuel injection device described in the Patent Literature 3, since fuel and air are not brought into collision with each other, it is impossible to make the spray penetration distance or the spray grain diameter variable at all. Thus, as is the case with the Patent Literatures 1 and 2, for attaining a combustion performance matching the start-up in the cold of an internal combustion engine or matching a partial load operation of the engine, it is impossible to make the spray penetration distance or the spray particle diameter variable and hence impossible to improve the combustion performance.